1. Field of the Invention
The present invention relates to system control equipment for railways, and more particularly, to a track circuit apparatus for a train using DS-CDM (Direct Sequence-Code Division Multiplexing), a kind of digital data communication, which divides a pair of rails into a plurality of block sections, prevents signal interference between adjacent block sections, fading, or noise in data communication between a ground-based transmitter and a ground-based receiver for each block section and data communication between an on-train controller of the train and the ground-based transmitter and receiver (controller), and provides high success rate of data communication and excellent data encryption performance.
2. Description of the Conventional Art
Typically, a track circuit apparatus refers to a circuit that uses rails upon which a train travels as a part of an electrical communication circuit to detect a train traveling on the rails, or a circuit apparatus that performs data communication between an on-train controller (to be mounted on the train) and a ground-based controller by using rails as a transmission line.
A conventional example of this track circuit apparatus will be described below with reference to FIGS. 1, 2, and 3.
As described above, a pair of rails 1 is divided into a plurality of block sections, and a power supply unit B1 and B2, a current limiter C1 and C2, and a track relay 100a and 100b are connected to the rails 1 for each block section. Although not shown, the track circuit apparatus may further include a ground-based transmitter and a ground-based receiver which serve as a ground-based controller and an on-train receiver serving as an on-train controller.
The power supply unit B1 and B2 supplies electric current to detect the presence of a train 50 on the rails 1.
The current limiter C1 and C2 is a device that limits current in order to protect damage to the power supply unit B1 and B2 caused by short-circuit current when a train is on the rails 1 and the two rails 1 are short-circuited by an axle 50a of the train 50. The current limiter C1 and C2 may include a resistor and a reactor.
If the train 50 is not on the rail 1, the track relay 100a and 100b is magnetized by the current supplied from the power supply unit B1 and B2. Otherwise, if the train 50 is on the rails 1, the two rails 1 are short-circuited by the axle 50a of the train 50. Thus, the current supply from the power supply unit B1 and B2 is stopped, and the track relay 100a and 100b is dropped (demagnetized).
Accordingly, the ground-based receiver (not shown) to be connected to the track relay 100a and 100b can determine the presence of the train 50 on the rails 1 depending on the magnetized state or dropped(demagnetized) state of the track relay 100a and 100b. 
According to one example of the conventional art, an example of a track circuit capable of transmitting and receiving data between the ground-based transmitter and the ground-based receiver or on-train receiver includes an audio frequency track circuit (hereinafter, abbreviated as AF track circuit).
In the AF track circuit (not shown), a ground control system (not shown) is installed on the ground for each block section, integrates information such as moving interval (distance) from preceding train, tunnel ahead, and the presence of a bridge to calculate a train speed for safe operation(that is moving) in a block section, performs frequency modulation (so-called “FM modulation”) on moving information data containing train moving information data, such as the calculated train speed for the block section, a predetermined gradient of the rails 1 in the block section, an effective length of the block section, and a line type indicating whether the block section is on the Gyeongbu line or on the Honam line, and transmits the moving information data by the ground-based transmitter.
The ground-based receiver is installed on the ground for each block section, and is in signal connection with the track relay 100a and 100b. The ground-based receiver determines the presence of the train 50 on the block section depending on whether the track relay 100a and 100b is magnetized or demagnetized.
The on-train receiver is mounted and installed on the train 50, and receives data from the ground-based transmitter. The on-train receiver receives a frequency modulation signal containing moving information data from the ground-based transmitter, extracts the moving information data by a demodulator included therein, and controls moving of the train such as speed acceleration or deceleration based on the moving information data.
For insulation between individual block sections in FIG. 1, a physical insulation method may be used, such as preventing interference with the conduction of current through the rails 1 by cutting predetermined lengths of the rails 1 without disturbing moving of the train at the boundary between each block section to form air gaps.
Referring to FIGS. 2 and 3, four different carrier frequencies are used to perform frequency modulation on signals containing moving information data with an audio frequency and transmit the data; two frequencies of 2,040 Hz and 2760 Hz are used in four block sections of rails of a southbound lane, and two frequencies of 2,400 Hz and 3,120 Hz are used in four block sections of rails of a northbound lane. The southbound lane and the northbound lane are adjacent to each other.
The reason why four different carrier frequencies are used is to prevent interference between data signals in communication between adjacent block sections in an upward or downward direction and prevent interference between data signals between two adjacent lanes of northbound and southbound.
The above-described track circuit apparatus according to the conventional art uses four carrier frequencies as above, for example, in four block sections of a northbound lane and four block sections of a southbound lane, the northbound lane and the southbound lane being adjacent to each other. Thus, the ground-based receiver or on-train receiver for each four block sections of the northbound and southbound lanes needs to be provided in four types. This incurs high cost of device configuration.
Moreover, the track circuit apparatus according to the conventional art may undergo signal interference from an adjacent block section, fading, or noise because of a channel environment that changes from moment to moment. In the event of signal distortion caused by such interference, noise, etc, error correction and restoration of digital signals have a 50% probability of 0 or 1 and are made possible by the use of a variety of mathematical algorithms; whereas error correction and restoration of analog signals are made difficult due to high signal variability. That is, it is difficult to perform error correction and restoration of analog signals distorted at the ground-based or on-train receiver.